This system is transparent because every container going on to the market has to be registered for the deposit. So the tally of recycled bottles and cans is based on real numbers, not estimates.

The packaging industry is urging ministers to stick with the current PRN scheme, which it says is cheaper. It is offering to make the system more transparent and to increase the amount raised for improving recycling.

The Environment Secretary Michael Gove is expected to make a decision on the issue after Easter.

Image caption
In Norway, a deposit-return machine accepts two types of plastic bottle

He said when packaging was placed on the market it is clean, dry and free from extra materials such as labels.

But when the quantity of plastic collected for recycling is measured, the weight is inflated by moisture, contaminants and labels.

Another problem may be that volumes of plastic packaging placed on the market are based on estimates provided by the packaging industry itself.

These firms, Eunomia claims, have little incentive to ensure accurate data because the more plastic they put on the market, the bigger their recycling bill through the PRN system.

EU comparison

The PRN operation is run by a group of compliance firms. The main operator is Valpak. Its spokesman, Adrian Hawkes, told BBC News there was no evidence of producers deliberately under-reporting their plastic production.

He said robust systems were in place to develop reasonable estimates of the total packaging placed on the market.

"We are confident in our information because it is based on very detailed and comprehensive data representing over 50% of UK packaged goods sales," he told BBC News.

"We use the UK's largest and most comprehensive database of packaging weights covering hundreds of thousands of different products to calculate the total tonnage of packaging put on the market."

But he did concede the report raised challenges over packaging associated with on-line purchases across borders - and the fact that some smaller businesses do not currently have to make a report.

He said their calculations were audited by the Environment Agency - and pointed out that providing false data is an offence.

Dr Hogg maintained that the audit system was not tight enough, adding: "The system of producer responsibility is failing. It has allowed problems with plastic packaging to grow."

He said reform of the producer responsibility system must form part of a more radical overhaul of waste policy.

And added that the PRN scheme was run at the lowest cost for business - not the lowest cost for society, because taxpayers have to foot the bill for collecting and disposing of waste.

"There should be a deposit refund scheme for beverage containers," he said. "And producers of other packaging should be charged fees that really reflect how much recycled material it contains, and how well it is recycled."

Local councils support a change in the system. The Local Government Association's spokesman, Cllr Martin Tett, told BBC News: "Councils support reforms that see producers take greater responsibility around the creation and disposal of waste - including making a contribution towards local authority costs.

"The UK raises the lowest level of contribution to costs from producers amongst all EU states."

'Kerbside success'

Valpak told BBC News: "The producer responsibility system was deliberately designed by government and industry to meet required recycling targets at minimum cost. It was not intended to cover all the costs (of recycling)."

A spokesman said it estimated that producers contributed £100m a year towards recycling - that's between 25% and 30% of what they estimate is the total recycling bill.

He said that Valpak had recently calculated that the situation is not so bad as it is portrayed. The current collection rate for plastic drinks containers in the UK is actually 74% - not the 57%, he said - thanks to kerbside collection systems.

He added that government was considering changes to the PRN system which could involve an increased cost share by producers to fund specific activities.

Samantha Harding from the Campaign to Protect Rural England told BBC News that packagers were "dangling the carrot" of more cash from an improved PRN system in order to avoid a deposit-return system.

"At the moment, 90% of costs fall on the taxpayer and this isn't right," she said.